1. The Technical Field
The present invention relates generally to watertight and airtight doors. More particularly, the present invention relates to dogging mechanisms for such doors.
2. The Prior Art
Watertight doors are well known in the art. Such doors commonly are used to prevent water infiltration from one compartment of a ship to another or from one area of a building to another. Such doors also can be used to prevent infiltration of air or other gas or vapor from one volume to another. A watertight door assembly typically comprises a door; a door frame; a hinge mechanism for pivoting the door about the door frame; a resilient, compressible seal for effecting a watertight seal between the door and the door frame; and a dogging mechanism for securing, or dogging, the door in the closed position against the door frame.
A dogging mechanism generally includes a number of dogs for pinning the closed door tightly against the compressible seal and the door frame via an actuator and linkage for engaging and disengaging the dogs. The dogging mechanism typically is attached either to the door or to the door frame. In applications where the dogging mechanism is attached to the door, manipulation of a door-mounted actuator and linkage causes dogs mounted on the door to engage with points about the perimeter of the door frame, thus pinning the door against the door frame. In applications where the dogging mechanism is attached to the door frame, manipulation of a frame-mounted actuator causes dogs mounted on the door frame to engage with points about the perimeter of the door, thus pinning the door against the door frame.
A dogging mechanism typically relies on friction in the mechanism and particularly between the dogs and the door/frame contact points to hold the dogs in the dogged position. Because the dogs rub against the door/frame contact points each time the dogging mechanism is actuated, the dogs and/or the engagement points on the door/frame wear over time. As the wear approaches a certain limit, the mechanism may lose its ability to hold the dogging mechanism in the dogged position by friction alone. Further, the mechanism eventually may cease to provide adequate compression of the resilient, compressible seal to afford watertightness. Consequently, conventional dogs and dogging mechanisms require regular, and in some cases frequent, maintenance to ensure proper functionality of the doors they are associated with.
Excessive force often is required to engage and disengage the dogs from the door/frame when securing and unsecuring the door, respectively. This force is transferred through the dog actuator mechanism to the operating handle. Gear reduction principles can be used to reduce the handle force required to operate the mechanism to a reasonable level. However, when gear reduction is used to decrease handle operating force, handle travel necessarily increases. Where allowable handle travel is a limiting factor, it might not be possible to reduce handle operating force to a reasonable level using gear reduction alone.
It therefore is an object of the invention to provide a novel watertight door assembly having a dogging mechanism which has the attributes of high reliability, low maintenance, reasonable operating force, and acceptable handle travel.
A watertight door according to a preferred embodiment of the invention includes a door, a door frame, a hinge or binges connecting the door to the door frame, a resilient compressible seal, and a dogging mechanism for securing the door to the door frame when the door is in the closed position. The dogging mechanism includes a number of dogs and an actuator and linkage for operating the dogs between a dogged and an undogged position. The dogging mechanism can be mounted on the door frame or on the door itself. Preferably, the dogging mechanism includes eight dogs, but more or fewer dogs can be provided. Preferably, a dog is located at each comer of the door and one or more dogs are located along each doorjamb. A dog can be, but need not be, located along each of the door header and door sill, as well.
In a first preferred embodiment of the invention, each of the dogs is a bar attached at one end to a pivot point on the door frame in a manner that allows the dog to rotate about the pivot point and against a corresponding contact location on the door. The contact location preferably is shaped so that the dog imparts a force on the door which increases with the dog""s rotational travel over the contact location This increasing force tends to compress the door against the door frame and the resilient, compressible seal therebetween.
Preferably, the rotating dogs of this embodiment are actuated using a chain-and-sprocket and bellcrank linkage mechanism, although other actuator mechanisms also can be used therewith. Each comer dog preferably is attached to a sprocket which can rotate in response to an appropriate force applied to the sprocket by a chain actuator. Each of the dogs located along the jambs, header, and/or sill preferably is attached to a bellcrank which causes the dog to rotate in response to an appropriate force applied to the bellcrank by a linkage mechanism.
In a second preferred embodiment of the invention, each of the dogs is a bar attached to the door frame in a manner that allows the dog to be actuated linearly in a direction which is substantially parallel to the plane of the door and substantially perpendicular to the edge of the door and door frame at the point of engagement. In this embodiment, each of the dogs is actuated so that the dog makes contact with and slides against a corresponding contact location on the door. The contact location preferably is shaped so the dog imparts a force on the door which increases with the dog""s linear travel over the contact location. As in the first preferred embodiment, this increasing force tends to compress the door against the door frame and the resilient, compressible seal therebetween.
Preferably, the linear dogs of this embodiment are actuated using a rack-and-pinion actuator mechanism, although other actuator mechanisms can be used therewith. Each linear dog preferably includes a toothed portion resembling a gear rack which engages with a corresponding pinion gear. Rotation of the pinion gear imparts linear motion to the linear dog, causing the linear dog to extend from the door frame towards the door or to retract from the door towards the door frame. Rotation is imparted to the pinion gear by the linear motion of a corresponding actuator gear rack. Preferably, the rack-and-pinion actuator mechanism forms a closed loop wherein all of the moving parts of the rack-and-pinion mechanism are interconnected.
In either of the foregoing embodiments, each dog preferably includes a roller element which rolls over the corresponding contact location on the door. The roller element reduces friction between the dog and the contact location and therefore reduces the force required to operate the dog actuator. The reduced friction forces between the dog and contact location reduce the tendency for friction alone to maintain the dog in the dogged position. To mitigate this effect, each contact location preferably is specially shaped to include a detent which cradles the roller element when the roller element is in the fully dogged position and therefore inhibits undesired undogging.